Glass lids of the above type completely fill the roof opening with all-round sealing in the closed position of the roof. When the vehicle is travelling, uplift forces that increase with increasing vehicle velocity act upon the glass lid. Because the lid is normally held only at its longitudinal sides at the sliding elements that engage into the guide rails fixed to the vehicle bodywork, it can bulge upwards above the roof contour as a result of these uplift forces. The arched form leads, especially at the front and rear edges of the roof opening because of the step formed there, to wind noise. Furthermore, the arched form of the lid leads to disadvantageous oblique settings of the lid holding and actuating elements at the connection points between the lateral edges of the lid and the guide rails. A dimensional increase in stiffening profiles attached to the lid to strengthen the lid cannot on its own guarantee adequate lid stability against the uplift forces in spite of a form-fitting and force-transmitting connection of stiffening profiles and glass pane to a cast-on or foamed-on lid border of plastics.
Furthermore, the maintenance of a lid curvature to correspond with the roof curvature, especially transverse roof curvature, is influenced by the different expansion behaviours of the glass pane and of stiffening profiles made of steel, resulting from heat produced in the casting-on or foaming-on of the plastics border in the mould and the subsequent cooling, after the finished lid has been removed from the mould.
In one known sliding roof of glass (G 90 16 831.3), of the above kind, it is proposed to form the reinforcing profiles of glass fibre, where the glass fibre may be constituted from long fibres, which can be bonded with a polyester resin to form the reinforcing profile. If glass fibre of this type is used for producing the reinforcing profiles, these profiles will be sufficiently stiff, so as to strengthen the lid, and because the glass fibre has the same coefficient of expansion as the glass pane, there will be no problem due to any difference in stress. On the other hand, however, the use of stiffening profiles made from steel is to be preferred, because the modulus of elasticity of steel is about three times that of glass fibre. For the purposes of this invention, however, not only steel is a suitable material, but also other metals which have a comparable elastic modulus.
The principal object of the present invention therefore is to provide a rigid lid for the roof opening of a vehicle, which shall retain its curvature adapted to the roof curvature even when uplift forces act upon it, and independently of the ambient temperatures that exist.